Plastic closure plug and container flange plug assembly



Nov. 29, 1960 A. J. STARR ET AL PLASTIC CLOSURE PLUG AND CONTAINERFLANGE PLUG ASSEMBLY Filed March 5, 1958 INVENTOR N ANTHONY J. STARRJEROME 5. HE /$LE R ALBERT HE/SLER ATTORNEY United States Patent PLASTICCLOSURE PLUG AND CONTAINER FLANGE PLUG ASSEMBLY Anthony J Starr, JeromeS. Heisler, 1234 Prospect Drive, and Albert Heisler, 117 W. 39th St.,all of Wilmington, DeL; said Anthony J. Starr assignor to Jerome S.Heisler and Albert Heisler Filed Mar. 5, 1958, Ser. No. 719,328

3 Claims. (Cl. 2 20-39.)

This invention relates to a plastic closure plug for'containers, andparticularly for polyethylene drums provided with one or more flangedopenings threaded to receive plugs of the same material.

Polyethylene possesses a number of desirable properties which commend itfor use as a material of construction in the manufacture of containersand the like for the transportation and storage of various materials,particularly valuable fluids and chemicals Which are corrosive or easilycontaminated if brought into contact with a metal surface. Polyethylenehas a relatively low density, is chemically inert, and in sheet or stripform is flexible, strong, practically unbreakable and'possesses hightear resistance. Moreover, since polyethylene is thermoplastic it lendsitself to fabrication into various shapes by procedures involving theapplication of heat.

Because of these and other desirable physical and chemical properties,polyethylene containers are becoming widely used in industryand-commerce. As in the case of conventional containers such as steeldrumsand the like, polyethylene containers are usually provided with oneor more openings for use in filling and emptying the container. Theseopenings are defined by flanges cooperating with suitable closures,preferably of the screw threaded type. Usually the flanges areinteriorly threaded to receive polyethylene plugs which are similarlyimpervious to the chemical to be deposited in the container. The flangesmay be additionally threaded on their outer walls to accommodatestandard metal or plastic screw caps which are economical enough to heexpendable. The plugs, on the other hand, are of a more expensiveconstruction because they are relied upon in-major part to provideeffective sealing closures for the drums and may be formed with acentral internally threaded flange to support a pouring device.Consequently it is of advantage if such plugs can be used repeatedlywith the containers for substantial periods of time.

The polyethylene plugs heretofore in use rely for their sealingqualities principally upon the conventional pipe thread with which suchplugs are provided. The sealing effect of this type of thread is due totwo factors: (l) the close fit of the apex of .the thread on the plugwith the bottom of the groove formed by the thread on the flange and (2)the fineness of the thread. As to the first factor, the seal.becomesprogressively less effective as the apex of the thread wears offthrough reuse. This deterioration of the seal is more rapid when thethread is made of a relatively soft material such as polyethylene. Alsothis type of material is more subject ltodamage in reuse than hardermaterials so that there is always the danger that in the handling offthe plug the thread will incur such damage as to destroy entirely itseffectiveness as a seal. With regard .to the size of the thread, theseal is more effective the finer the thread size. To make the seal ofthese prior polyethylene-plugs as efiective as possible, the threadsthereof have been made relatively 2,962,185 P tented Nov- .22. 1%!

fine- -of the order of approximately 11 threads per inch, Threads ofsuch fineness, when made of a soft material like polyethylene, wear outrapidly and provide'a poof seal after little usage of the same.

These prior polyethylene plugs also have been pros vided with sealingflanges. According to onetype of cone. struction, the sealing surface,of the flange is curved in a transverse direction to enable it to seatsntigly on acurved, annular sealing surface provided on the outer end ofthe drum flange. The effectiveness of the seal produced by such partsdepends on the wiping wedging action of the sealing surface of the plugon' the sealingsurfa ceof the flange as the plug is screwed tightlyinto'place. Sucha seal is difficult to obtain repeatedly when sealingparts having the aforesaid construction are made of polyethylene whichis soft and therefore subject to rapid wear under stresses of this type.Polyethylene is also of such a compressible and yielding nature thatrather than afford a more secure seal as the plug is so tightened on thedrum flange, it will have: a tendency to give to such extent that twosurfaces of the construction indicated will properly coact to producethe seal they were designed to effect. Further, under the pressuresusually applied in fitting such a plug into closed position in theflange, the polyethylene material in the root portion of an out: Wardlyextending'sealing flange of the plu g will tend to cold flow to cause apermanent deformation of the flange, thereby rendering the flangeuseless as a sealing device.

In another type of polyethylene plug, theflange thereof is provided onits underside with an annular head which is located adjacently to theperipheryof such flange and which is adapted to seat'in a groove on theend of the drum flange. The sealing effect of this arrangement isdependent upon theflclose fitting of the bead within the groove and theclose seating of the end of the bead on the inner wall of the groove.Because of the yielding nature of polyethylene, however, the peripheraledge POT.- tion of the flange containing the bead will give as the plugis screwed tightly into place, thereby destroying the sealingarrangement which the bead and groove are designed to effect. In thisconstruction also, thecold flow of the polyethylene material in theflange under the applied pressure will tend to cause a permanent set ofthe flange in a tilted condition. Also because of 'the softness ofpolyethylene, the bead on the plug will enlarge the groove on the drumflange and itself Will wear as the plug is reused, thus destroying thesealing effect of such two parts. Further, because of the relativelyrapid wear of the fine conventional .pipe threads provided on the plugand-flange of this construction, it is difficult to maintain a positive,tight connection between the engaging surface portions of these threadssuch as to produce repeatedly o d seals be e e p g an the containerflange at the outer end of the latter.

It is the primary object of this invention to proyide a closure plugmade of polyethylene, polyisobutylene and like materials that is capableof forming an effective seal on the flange of a polyethylene containerand which is of such improved construction that his not subject to thedisadvantages of the above discussed plug construe,- tions and,therefore, may be reused for considerable periods without deteriorationof its sealing capabilities.

The novelty of the closure plngof this invention resides in part in theaccomplishment of its sealing action .primarily .at the top of thecontainer flange with the aid of a buttress'type of thread provided onthe exterior of the plug and adapted to interengage with a correspondingbuttress-type-thread providedon the interior wall of the containerflange. In accordance with one of thejfeatures of the invention, theunder sealing surface of the flange .is made flat and disposed atrightangles to'the' central axis of the plug and in opposed relation toa flat annular sealing surface provided on the top end wall of thecontainer flange. The sealing surface of the plug coacts with thesealing surface of the flange either directly, or through an annulargasket made of any suitable plastic material such as polyethylerieorrubber and preferably made of a softer material than the materials ofthe plug and the container flange. In accordance with another feature ofthe invention, the gasket is provided with the general shape of a fiatring and is provided adjacent its inner and outer peripheries, on bothsides thereof, with small ring-shaped beads. Thus, when the plug isfitted into the container flange, the beads on the upper side of thegasket are in engagement with the sealing surface of the plug and thebeads on the lower side of the gasket are in engagement with the sealingsurface on the flange, such beads providing the seal between suchsealing surfaces.

The seal between the plug and the container flange is further insured bythe interaction of the spiralling surfaces of the buttress threads ofthe plug and flange which are disposed at right angles to the centralaxes of such members. Initially in seating the plug the gasket willrotate with the plug. When, however, the gasket is pressed intoengagement with the container flange sealing surface to a degree thatthe frictional resistance therebetween becomes as great as the rotativecomponent of the force thatis applied to the outer edges of the beads ofthe gasket by the plug sealing surface, the gasket will stop its rotarymovement as the plug is turned. Thereafter, the axial thrust componentonly of the forces resulting from the interaction of said threadsurfaces will be transmitted to the flange sealing surface through thegasket. Thus, during the final turns of the plug to bring it to a sealedcondition with relation to the container flange there is no rotationalmotion between the gasket and the container flange sealing surface, thesealed condition between such parts being attained by force appliedlongitudinally of the container flange. The combined effect of suchinteraction of the thread surfaces, the flange sealing surfaces and thegasket is a positive sealing action whereby wear of the flange sealingsurface is minimized to such an extent that good sealing results can beattained repeatedly. The gasket being of softer material than thematerials of the container flange and the plug will absorb the greatestwear and it is economical enough to be expendable. Further, as the beadson the gasket enable the forces that are applied by the plug flange tobe distributed more uniformly to the gasket and to the container flangeseating surface without any substantial levering effects on the plugflange, any tendency of the latter to tilt from normal position isminimized.

In accordance with another feature of the invention, the buttressthreads of the plug and flange provide a secondary seal between thespiral surfaces thereof which are disposed perpendicularly to thelongitudinal axis of the flange. The seal effected by such spiralsurfaces of the buttress threads is not dependent upon the previouslyexplained end of the thread engagement required with the conventionalpipe thread to provide a good seal, nor is it dependent upon thefineness of the thread. The buttress thread, therefore, can be madesubstantially more rugged and heavier than the conventional pipe threadto bring it more into conformance from a practical standpoint with thepolyethylene material of which the plug and flange are formed. With amore rugged thread, the spiral surfaces can be made substantially widerthus providing better sealing surfaces and enabling the provision of abetter seal with a substantially lesser number of thread turns than ispossible with the conventional pipe thread. It has been foundsatisfactory to use a buttress type thread having less than one half thenumber of threads per inch which would be required in a plug having theconventional pipe thread. Since the sealing effect of the buttressthreads is not dependent on 'an end of 4 the thread engagement asrequired in conventional pipe threads, wear of the thread ends does notdestroy the seal. Further, while the camming surfaces of the heavierbuttress threads will wear to some extent during usage, such wear willtake place on the strongest part of the thread and will therefore beminimized. Such wear as will occur will not be suflicient to effectsubstantially either the seal of such camming surfaces, or the sealbetween the sealing surfaces of the plug and flange due to the gasket.

A more complete understanding of the invention will be obtained from thefollowing description, when read in connection with the accompanyingdrawings, in which Fig. 1 is an exploded view of a closure plug made inaccordance with the invention and including the plug with its sealinggasket and a screw plug for the threaded opening to which a pouringdevice may be connected, each of said parts being shown in centralvertical section.

Fig. 2 is a central vertical section through the flange portion of acontainer with the plug and gasket unit in seated relation thereto.

In the drawings, there is shown a fragmentary portion of the top end ofa polyethylene drum type container 10 provided with the usual flange 11defining the opening by which the drum may be filled or emptied. Theflange is provided with an external screw thread 12 to which may beattached a standard metal or plastic screw cap (not shown) and isprovided with an internal screw thread 13 into which is screwed the plugof this invention. The screw thread 13 is of the buttress type and has adownwardly spiralling thread surface 14 disposed at right angles to thecentral axis of flange 11 and facing downwardly in opposed relation tothe interior of the container. The thread 13 is complemental to theexterior thread on the plug which will be described later in moredetail. The flange is provided at its upper end with a flat annularsealing surface 15 which is disposed at right angles to the central axisthereof. The flange 11 is made of polyethylene and may be formed in themanner disclosed in pending US. application Serial No. 375,625, filedAugust 21, 1953, utilizing a similar mold assembly. In practicing theprocess disclosed in said application to mold flange 11, it iscontemplated using polyethylenes having a density within the range ofapproximately 0.92 to 0.95, such as the polyethylene known as SuperDylan manufactured by Koppers Co., to assure that the thread 13 and thesealing surface 15 have sufiicient hardness to reduce wear thereof tothe extent that such parts shall be enabled to properly perform theirintended functions throughout the life of the drum.

The plug unit, as shown in Fig. 1, includes a plug which is indicatedgenerally by the reference numeral 20, a gasket 21 and a stopper 22. Theplug 20 may be formed in accordance with the process disclosed in saidUS. application Serial No. 375,625, utilizing a mold assembly permittingthe practice of such process and employing a polyethylene having adensity wtihin the range of approximately 0.92 to 0.95 to provide amolded polyethylene plug of suitable hardness. The plug 20 comprises acylindrical shank 23 formed to provide an external screw thread 24 ofthe buttress type. The thread 24 includes a downwardly spiralling threadsurface 25 disposed at right angles tothe central axis of the plug andfacing upwardly in opposed relation to the thread surface 14 of thethread 13 on flange 11 (note Fig. 2). The thread surface 25 extendsoutwardly from the bottom edge of a longitudinally disposed threadsurface 26 which spirals about the central axis of the plug and formsthe bottom of the groove between the. thread turns. The outer peripheryof the thread surface 25 forms a spirally-shaped line of juncture withthe top edge of longitudinally disposed spiral thread surface 27 formingthe outer edge of thread 24. The bottom edge of thread surface 27 isjoined to the upper edge of an inclined spiral thread surface 28 whichat its lower edge is joined to the top edge of thread surface 26.Buttress thread 24. therefore is rugged in construction and has arelatively blunt outer edge that can withstand substantial wear.Preferably in a plug of the type indicated, the thread 24 is made withapproximately 5 turns per inch and with a thread surface 25approximately inch to provide a heavy thread with a wide working surfacefor engagement with the similarly constructedsurfa'ce14 of flange thread13. When the plug 20 is in closed position on flange 11, the engagedthread surfaces 14 and 25 form a suitable sealing means. This seal, ashas previously been indicated, is more effective when such surfaces 14and 25 are relatively wide. Consequently, by making the said engagingsurfaces approximately A; inch wide, the number of thread turnsnecessary to provide an effective fluid-tight seal is considerablyreduced. This in turn enables the threads to be made heavy enough towithstand wear without substantial loss of their sealing qualities for along period of usage even when made of a relatively soft material suchas polyethylene.

Integral with the top of the shank 23 is a flanged .top 30 having anoutwardly extending sealing flange 31. Provided on the underside offlange 31 is an annular sealing surface 32 which is flat and disposed.at right angles to the central axis of the plug so as to be positionedin parallel opposed relation with the flat annular sealing surfaceprovided on the top end of flange 11. This sealing surface is not widewith relation to the thickness of the flange 31 being approximately inchwide when the flange is approximately /8 inch thick. Thus, if thelongitudinal stresses to which sealing surface 32 is likely to besubjected in the use of the plug, are effectively distributed withrelation to such sealing surface, the chances of flange 31 becomingtitled or deformed as a result of such use are not great and are withinpractical considerations. Such an effective distribution of the stressesmay be accomplished by use of a gasket such as the gasket 21 shown inthe drawings. Gasket 21 is formed of a resilient and compressiblematerial such as rubber or a polyethylene having a density ofapproximately 0.92. Thus gasket 21 has a hardness substantially lessthan that of the materials of flange 11 and plug and while it has athickness approaching that of flange 31, approximately ,5, inch, flange11 is substantially rigid, whereas gasket 21 is relatively flexible.Gasket 21 has a width substantially the same as the width of flangesurface 32, namely, inch. Adjacent to each peripheral edge of gasket 21,and on both sides thereof, is a ring-shaped bead 34 having a width ofapproximately inch and a thickness of approximately inch. Thus anystresses applied to the flange 31, are transmitted through the morecompressible material of the gasket by way of the beads 34, one pair ofwhich is located adjacently to the root of such flange and the otherpair of which is located adjacently to the outer edge of such flange.The upper concentrically arranged pair of beads in engagement with thesealing surface 32 of the flange and the lower concentrically arrangedpair of beads in engagement with the sealing surface 15 of the containerflange, become flattened under the stresses imparted in screwing theplug to seating relation to the flange and together with such surfacesform the primary liquid-tight seal between the plug and the containerflange. Because of the compressible nature of the material of gasket 21any irregularities or worn spots in the sealing surfaces 15 and 32 willbe conformed to. by such material without weakening the overalleffectiveness of the seal. Further, this quality of the gasket will tendto maintain an effective sealing relation between the working threadsurfaces 14 and 25 even when such surfaces have become substantiallyworn.

The flanged top is provided with a central circular opening whichextends down into the upper end portion of the shank 23. Communicatingwith the bottom end of such opening is the upper end of a socket 36provided with an internal thread 37 and closed at its lower end by adiaphragm 38. Th diaphragm is at substali tially reduced thickness toenable it to be readily. severed from the body of the. plug 29 when thecontents of the container are to be dispensed. The socket 36 is Providedat its upper, open end with a smooth, curved, outwardly extendingsealing lip 39. The outer peripheral edge of the lip 39 is integrallyconnected with the lower end of the annular wall 40 forming the opening35. Provided in the wall 40 above the sealing lip 39 are two opposedpairs of slots which are open at their upper ends and which provideopenings through wall 40 into the tool engaging recesses 41 formed inthe top portion of the plug in offset relation to the central opening 35thereof.

While there is hereinabove described and illustrated in the accompanyingdrawings a preferred embodiment of the invention, it will be apparent tothose skilled in the art that changes may be made therein withoutdepart.- ing from the spirit of the invention or the scope of theappended claims.

We claim: l. A closure plug for a drum made of polyethylene or the likeand provided'with an Opening defined by a flange of similar materialhaving an annular sealing surface at the top end and an internal screwthread, said plug being constituted of polyethyleneor similarthermoplastic material having relatively soft and yielding qualities anda tendency to cold flow into a permanently deformed set under sustainedpressure, said plug having a tubular shank with an external screw threadformed in the tubular body thereof and having at the top of such tubularshank a sealing flange extending outwardly from the outer cylindricalsurface of said tubular shank and provided on its under side with anannular sealing surface coactable with the sealing surface at the topend of said drum flange to effect a seal therebetween, the annularprojecting portion of said plug flange being of considerable thicknessto prevent substantial deformation of the polyethylene material thereofunder the pressures required to effect such seal, and the sealingsurface on said plug flange being flat and disposed substantially atright angles to the central axis of the plug, an annular gasket in theform of a flat ring surrounding said plug shank adjacent to said flangesealing surface thereof, said gasket being made of a resilient,compressible material that is softer than the polyethylene materials ofwhich said plug flange and drum flange are constituted so that pressuresapplied to said plug to form a seal are distributed to the drum flangewith substantial uniformity and without any substantial levering effectson the plug flange so that a good seal is enabled to be made withoutexerting substantial distorting force on the plug flange, the screwthread on the plug being of the buttress type and being recessed in thetubular shank so that the outer edge of such thread lies in the outercylindrical surface of said tubular shank, said thread in transversecrosssection having an upwardly disposed side positioned substantiallyat right angles to the central axis of the plug and in parallelism withsaid plug flange sealing surface and directed in opposed relation to thelatter so that as said plug flange sealing surface compresses saidgasket into sealing relation on said drum flange sealing surface, saidupwardly disposed side of said screw thread moves into engagement withthe associated downwardly disposed side of the internal screw thread onsaid container flange and under the pressures applied in effecting suchseal the polyethylene materials of such sides are displaced to be lockedtogether into tight substantially uniform contact affording equaldistribution throughout the length of said thread outward forces actingthereon, said buttress thread being of relatively few turns and beingrelatively heavy and massive with a blunt substantially wide outer edgeand with a thickness at its base at least as great as the thickness ofsaid plug flange to give it sufficient ruggedness to prevent rupture ofsuch seal by distortion of the polyethylene material of such threadunder outward 'forces acting on such plug and to prevent for aconsiderable period of repeated usage cold flow of the polyethylenematerial forming said upwardly disposed side thereof to the extent underthe pressures required to effect said seal that resulting deformation ofsuch thread side would substantially lessen the etfectiveness of suchseal.

2. A closure plug such as defined in claim 1, in which said gasket isprovided on both the upper and lower surfaces thereof with twoconcentric substantially spaced beads arranged adjacently to the innerand outer peripheries of said gasket, said beads being of such heightthat they engage the sealing surfaces on said plug and drum flanges toform the seal therebetween, the beads on the upper surface of saidgasket being paired with the beads on the lower surface of such gasketso that the forces applied to said plug in forming such seal aretransmitted directly through such paired beads and without deformationof the body of such gasket between such paired beads in a direction atright angles to the axis of said plug.

3. A closure plug such as defined in claim 1, in which said plug has aninternally threaded tubular passage to threadedly receive a stopperlocated within the tubular shank thereof and concentric thereto, saidtubular passage being supported in spaced relation within said shank bya top flange integrally connected at its outerperiphcry with said plugsealing flange and integrally connected at its inner periphery with theouter end of said tubular passage by means of an annular stopper sealinglip which is curved downwardly in transverse cross-section,

and in which said plug includes a stopper having an external thread tobe threadedly received by said tubular passage and having a curvedannular surface engageable with said sealing lip to effect a sealtherebetween when said stopper is screwed into said tubular passage, theinterior of said plug sealing flange above said top flange beingconfigured to provide tool engaging means.

References Cited in the file of this patent UNITED STATES PATENTS

